Questions tagged [space-expansion]
The expansion of the universe is a phenomenon wherein, at scales much larger than galaxies, the distance between objects grows over time. This phenomenon is often described as "expansion of space", although there is no difference between space expanding and objects moving apart.
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Viable values for the 'K' parameter in the FLRW metric
The FLWR metric is sometimes given as $$c^2 d\tau^2 = c^2 dt^2 - \frac{a(t)^2}{(1-KX^2)} dX^2. $$
I am not interested in the tangential motion so I set $d \Omega = 0$ although it is of interest in ...
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Can a light signal from Earth reach a galaxy outside the Hubble Horizon?
Is this video on the FLRW metric (timestamp 19:00 minutes) mistaken in its claim that a light signal from Earth cannot catch up with a galaxy outside the Hubble horizon, due to the horizon receding at ...
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Friedmann Equation and a contracting universe
Consider a universe with a nonzero curvature and matter.
One can write the Friedmann Equation in this universe as such:
$$\frac{H(t)^2}{H_0^2} = \frac{\Omega_0}{a^3}+\frac{1-\Omega_0}{a^2}$$
Where $H(...
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Simple question about finite Universe [duplicate]
If, by Big Bang, Universe was created from initial singularity, with finite "speed" of expansion of matter, shouldnt it be finite as well?
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Understanding expansion of the Universe as things flying apart
Say that we have a Universe uniformly filled just with matter (let's not bring dark energy into this). And say that we fill it with very light particles (so that the gravitational interaction between ...
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Is it true that $\dot{H}(t)\sim H(t)$, and if so, why?
In the context of working with the FRW metric in Cosmology, I'm trying to reproduce the results of a paper where an expansion of the metric in terms of perturbations is performed. The author gives a ...
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Does gravitational redshift conserve energy?
It is claimed that redshift due to cosmological expansion doesn't conserve energy. Does this exception also apply to gravitational redshift? Why or why not?
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Please help me with this paradox [closed]
Physicists believe that some galaxies are moving away from us at faster than the speed of light. A galaxy that is moving away from us at faster than the speed of light would be moving backwards in ...
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Does the expansion of the universe cause the universe reach maximum entropy faster than a non expanding universe?
I've seen Does an expanding universe cool down?
So I understand an expanding universe cools down, my question is, does an expanding universe reach maximum entropy faster than a non-expanding universe?
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Negative Horizon distance
Consider a flat universe, here, proper distance can be given by R-W Metric:
$$d_p (t_0) = c\int_{t_e}^{t_0}\frac{dt}{a(t)},$$ $t_e$ is the time when a photon is emitted from a distant galaxy, $t_0$ is ...
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